Organizations that embrace cloud computing outsource massive amounts of data to external storage providers. Cost savings, lower management overhead, and elasticity are just some of the attractions of the cloud. But cloud computing entails a sacrifice of control. Tenants give up configuration and management oversight of the infrastructure that contains their computing resources. In cloud storage systems today, for example, tenants can only discover corruption or loss of their data (particularly infrequently accessed data) if their service providers faithfully report failures or security lapses—or when a system failure occurs. This integrity-measurement gap creates business risk and complicates compliance with regulatory requirements.